1. Field of the Invention
The present invention relates to a wireless response device and an image forming apparatus and electronic equipment using the wireless response device.
2. Description of the Related Art
Status detection sensors for detecting equipment status are widely used in electronic equipment such as copiers and printers. As status detection sensors, for example, switches that detect status with an electrical short circuit or release, and photo interrupters that detect status by the interruption or transmission of light, are used. Status detection sensors are often used in applications that detect the binary status of whether or not a paper has passed, as in the case of a paper passage sensor, for example. In this case, the electronic equipment performs operating control and status monitoring of the electronic equipment according to the detection results of the paper passage sensor.
JP 2004-32052A discloses a wireless sensor (wireless response device) that detects the open/closed status in an opening/closing portion of a piece of equipment. This wireless sensor detects the open/closed status of the opening/closing portion by changing the state of electromagnetic waves of the equipment by placing the conductor in the vicinity of an antenna. Also, in Non-patent Document 1 (L. Reindl, et. al, Ultrasonics Symposium Proceedings, Institute of Electrical and Electronics Engineers (IEEE), SAW Devices as Wireless Passive Sensors, 1996, p. 363-367) and Non-patent Document 2 (F. Schmidt, et. al, Ultrasonics Symposium Proceedings, Institute of Electrical and Electronics Engineers (IEEE), Remote Sensing of Physical Parameters By Means of Passive Surface Acoustic Wave Devices (“ID-Tags”), 1994, p. 589-592), wireless sensors using a so-called SAW-ID (Surface Acoustic Wave Identification) are disclosed.
In status detection sensors such as switches and photo interrupters, power supply and the sending and receiving of signals are ordinarily performed by wire. When using a power line, there is the problem that power is also consumed when the equipment is in standby, or that malfunctions occur due to noise mixing in from the power line. Further, there is the problem that wiring becomes complicated when many status detection sensors are used in one piece of equipment, and many man-hours become necessary during fabrication or maintenance. Also, there is the problem that with connectors using the so-called lead-free materials of recent years, stable propagation of signals is hindered by the deterioration of those materials over time.
In order to address the problems described above, it is conceivable to wirelessly send and receive data signals to and from the status detection sensor. However, it is necessary for ordinary wireless communications equipment to have a battery inside in order to supply power. Thus, there is the problem that considerable labor is needed when exchanging batteries, so the realization of that concept is difficult. Also, as disclosed in JP 2004-32052A, in a system using RFID (Radio Frequency Identification), which does not require a battery, a communications blocking antenna for absorbing electromagnetic waves from an RFID reader is brought near or moved away from an RFID chip in order to not allow the RFID chip to operate. This system uses a principle in which the RDIF chip operates when the communications blocking antenna is moved away because electromagnetic waves reach the RFID chip, and the RDIF chip does not operate when the communications blocking antenna is brought near because electromagnetic waves are absorbed by the blocking antenna. However, in order to clearly change signals, a large space is necessary to bring the communications blocking antenna near and move it away. In this manner, the technology disclosed in JP 2004-32052A has the problem that it can not be used as a status detection sensor provided in a small space, such as a paper passage sensor, for example. Also, the wireless sensors disclosed in Non-patent Documents 1 and 2 have the problem that they have a configuration in which they have been specialized into a SAW device, which, in comparison to an RFID chip formed by a semiconductor (see FIG. 11 of Non-patent Document 1, and FIG. 6 of Non-patent Document 2), is disadvantageous for handling a large number of IDs. Further, when using a contact switch, as disclosed in Non-patent Document 2, there is the problem that depending on the arrangement of the SAW reflector, useless noise is generated because chattering occurs. Still further, when a sensor, which functions as a variable impedance, is arranged on a reflector disclosed in Non-patent Document 2, it is necessary to measure changes in amplitude of signals from the reflector. Therefore, a problem arises to apply the technology for a frequency band where an intensity of a signal is limited.